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| Typical continuous miner |
Background
The demand for larger, more-powerful mining equipment stimulated the need for increased voltages for coal mine face machinery. Higher-voltage equipment can supply more power without requiring larger, heavier trailing cables. Special design, use, and maintenance precautions are needed to ensure an equivalent level of safety when high-voltage systems are used in permissible areas. Since 1997, which was before each continuous mining machine operating above 1000-V ac could be put into use, MSHA required a Petition for Modification, and each individual machine was then scrutinized prior to approval.
NIOSH research indicated that higher voltages were indeed feasible with appropriate precautions. Several NIOSH research reports provided technical information used by MSHA to help formulate new regulations that would allow the use of high-voltage longwall machines in coal mines (Final Rule, 30 CFR Parts 18 and 75, “Electric Motor-Driven Mine Equipment and Accessories and High-Voltage Longwall Equipment Standards for Underground Coal Mines” on March 11, 2002. Published in Federal Register, Vol. 67, No. 47, March 11, 2002, Rules and Regulations, pp. 10972-11005). These reports also provided technical information critical to the development of the proposed high-voltage continuous miner rule. Such information included enclosure pressures developed during electrical arcing up to 15 kV in methane-air atmospheres, as well as recommendations for high-voltage electrical creepage and clearance distances, design criteria for explosion-proof enclosures, and permissibility hazard reduction.
Potential Outcome
The proposed rule “High-Voltage Continuous Mining Machines,” RIN 1219-AB34, published by MSHA in the Federal Register of July 16, 2004 (Vol. 69, No. 136, Proposed Rules, pp. 42811-42840), is anticipated to become law by 2010. The new rule will eliminate the need for each new high-voltage continuous mining machine to undergo the Petition for Modification process. The proposed rule draws on the results of NIOSH research to allow the safe use of explosion-proof continuous miners. The ability to accept high-voltage, continuous-mining-type machines removes a significant barrier to safer, more efficient, and economic coal mining in the United States.